OK, my Bobbie is an indoor only kitty. She's almost 14, and she's never been outside. Our old house was on a really busy road, so the RSPCA said we could only have a cat from them that was an 'indoor' cat. They said they don't get many of them, and expect to wait for a while... the next weekend, they phoned and asked us if we wanted to come and see Bobbie - she was 5 years old at the time :)
We wanted another cat also, but she will not let us. We were told that the reason she was looking for a new home is because 2 people moved in together, and they both had cats... Bobbie kept starting fights with the other cat, so that's they story of why they got rid of her :( - she will not accept any other cats (or dogs) in the house (she beat up my mums dog, when she brought it over once). she is very tiny, so we think that she was a runt, and had to fight for food, and now doesn;t want to share with others!
She likes to look out the window, but you can leave the door open, and she will just look, and sniff, but not actually go outside.
So, our paticular cat is very happy being the only cat in the house, loves it in fact. And she is perfectly happy just staying inside, being lazy as hell. Being the only animal, she does require a lot of human attention, and is a bit needy sometimes, but we like her that way :)
Also, on the plus side, she never gets fleas, in fights with other kittys, or lost, or anything like that :)